Thyratron tube



H. B. SLOAN THYRATRON TUBE Dec. 2 7, 1949 2 Sheets-Sheet l Filed March29, 1945 INVENTOR.

ArroR/vfy Dec. 27, 1949 l H, B. SLQAN 2,492,665

THYRATRON TUBE IN VEN TOR.

HOWARD SLon/V Patented Dec. 27, 1949 UNITED STATES PATENT oFFlCETHYRATRON TUBE Howard B. Sloan, Swampscott, Mass., assigner to SylvaniaElectric Products Inc., Salem, Mass., a. corporation of MassachusettsApplication March 29, 1945, Serial No. 585,491

Claims. (Cl. Z50-27.5)

This invention relates to thyratrons, and particularly tohydrogen-filled thyratrons.

Objects of the invention are the production of short sharp pulses, theprevention of undesirable iiash overs, and the prevention of clean up ofthe gas in the bulb.

These objects are obtainedby the use of hydrogen as a gas filling, abeaded. anode lead with a separate enclosing insulating tube, and theuse of a cathode coated on its sides only, with its sides surrounded bya shield spaced reasonably closely thereto. The device is especiallyeffective when the electron current carried by the tube is in excess ofthe normal thermionic emission of the cathode.

The invention Will be described with reference to the accompanyingdrawings, in order to make clearer further objects, advantages andfeatures of the invention.

Figure l shows a section perspective of a tube according to theinvention;

Figure 2 shows a seal which is one embodiment of the invention; and

Figure 3 shows a longitudinal section through the center of the tube.

In the iigures, the glass tube I has the lead-in wire 2 sealed throughand closing one of its ends with the stem 3 through which additionallead-in wires 4, 5, and 6 extend, sealed to and closing the oppositeend. The tungsten lament coil 1. is attached at one end to the conductor8 which supports it from the lead-in wire 5 to which it is electricallyconnected. A coating of refractoryv insulating material such as aluminumoxide is used on the lament turns to prevent short-circuiting thereof onsagging. The other end of filament coil 1 is connected by the metal tabs9 and I9 to the disc II whose anged edges I2 are attached to nickelcylinder I3, which is coated on its outside diameter with an electronemitting mixture of barium and strontium oxides. This coating is bestterminated a short distance from each end of the cylinder. The bottom ofthe cylinder is attached by the disc I4 through which the conductor 8passes and from which it is spaced or insulated. A disc of largerdiameter i5 is attached to the disc I4 and extends beyond the diameterof the cathode I3, to support the cathode shields I6 and I1 which may beattached to the flange or rim I3 at the outside of the disc. The twocathode shields are preferably spaced apart a short distance. The collarI9 supported from the top of shield I1 in turn supports the shieldingdiscs 29, 2l and 22 which are spaced from each other and attached to thecollar i9 2 by the conductors 23 and 24. The cathode shields IIS and I1may be supported by the wires 25 and 26 extending from a collar 2'Iaround the base of stem 3, to insure rigidity.

Anode 28 is a circular metal disc attached to and supported by thelead-in wire 2 over which the glass sheath 29 is sealed, extending fromseal 30 to a point close enough to the anode 28 to prevent flash over.The glass tube 3| concentric with the sheath and spaced therefrom,extends along the entire length of the sheath and merges with the sheathinto the seal 30 through which the lead-in wire 2 extends to be attachedto the contact 32 by the solder 33. A collar 34 around the free end ofglass tube 3| is attached to the transverse disc 35 which shields thetop of the anode 28. The grid 36 of metal gauze is attached to theflange edge 31 of disc 35 at the top of anode 28 and to the collar` 38below anode 28. The perforated disc or grid 39 is alixed to the collar38. The additional spider 49 connects the disc shield 4I to the grid 39and spaces it therefrom. The construction of the spider 4U provides anelectron path around the periphery of the disc shield 4|. The anode 28is thus completely surrounded by a structure comprising the grids 36 and39 through .which electrons from the cathode I3 must pass to reach saidanode 28. The spacing between the anode 28 and the various parts of thegrid should be small enough to prevent ilash back between the parts. Theshielding disc 4l serves to prevent any metal evaporated from the lamentfrom depositing on the grid 39 and causing it to emit electrons. For themost part however, the material evaporated from the cathode I3 will bedeposited on the shield I6 concentric with the cathode.

The bottom part of the grid 36 is attached to the metal cylinder 42which helps to support it and also acts as additional heat shield forthe cathode I3. Cylinder 42 is supported at its bottom by the wires 43and 44 which are sealed into stem 3. The conducting ribbons 45 and 46connect lead-in wires 43 and 44 with the cylinder 42 to insure goodelectrical contacts therewith. Tabs such as 4l may be used to assist inconnecting lead-in wires 43 and 44 to the cylinder 42. Similar tabs 48may be used to aid in connecting shield I1 to its support wires 25 and26. The base 49 may be cemented to the bottom part of the tube I by thecement 56 and the lead-in wires 4, 5, and 6 may be connected to thecontact prongs 5I, 52, 53, 54 of the base which :are insulated from eachother. Prong 52 may be connected inside the base to prong I by thejumper connection 55.

The tube is of course evacuated and lled with hydrogen at a pressure of0.6 mm., for example.

In operation current is passed through the filament I which serves toheat the nickel cylinder 43 and the emitting coating ,upon it. Theelectrons emitted therefrom pass through ,the gas in the tube andeventually through the grids 36 and 39 to reach the anode 28. The grids3B and 39 can thus be used to control the starting of the discharge asin the usual thyratrons and 'b e- .cause of the use of hydrogen asthegas filling the discharge will deionize rapidly when the anodevoltage is removed.

Prior to my invention the clean up of hydrogen in tubes of this sort wasla serious problem. I find that in a tube of my novel constructionhowever, the hydrogen .is not cleaned up appreciably. This appears to bedue to the fact that kthe electrons are all emitted "from ithe outsideof the cylinder |73 and passed Vthrough the confined space lbetween thecylinder and the shield. Barium or strontium particles .sputtered fromthe vcathode will lbe picked up by the jinside surface .of the shieldgli. Ihe combination of these barium Aand strontium particles with thehydrogen to form a 'hydride may b e the. cause of .the .hydrogen cleanup and in my .particular construction .the particles fall on the shieldclose to the cathode. .apparently under such equilibrium conditions as.cause the hydrogen tobe removed therefrom. The absence of cathodecoating from the top .I2 `of .the cathode insures. that .all thesp11ttere-d particles .will .come rfrom the sides of the cathode. Invtubes prior to my .invention they sputtered particles ,appear .to havehad a comparatively free path y.tl-wouah .the interior of the tube.

I ndalso thatit .is Well ,to l operate .the tube at Y.currents .in.excess .0f .the .normal `thenmionic electron emission of the cathodefor the .ternperature .at .which it soperated. For example.. thecylinder .i3 may lhave a diameter of inch and a height of l1/,1 inches,with an uncoated Space of 0.4 om. at Ieach end of .the cylinder. Thisgives a coated area of about la cmiior the barium and .strontium .oxidecoating; and yet peak currents as high Aas k3.50 amperes. may vbe safelyVcarried .by the Itube without .reducing ,its life below the presentrating .o f `50.0 hours. Actually .I have Vfound a coating area.extending from a point 0. 4 `cm. from the top of the cylinder l5 for adistance of 0.8 om. downward to be sufcient for such a life.

A'The anode 28 and its surrounding grid structures 55--35-38 are spacedquite closely together, for example, 0.80 inch, and will not -ilash overwith the gas pressure used, because of the well known short-pathprinciple. However, Vwere it not for the sheath 2-9, liiash over couldoccur between the grid structure 35, 36, V39 'and the more remote partsof the lead-in wire 2 inside the tube. The sheath prevents this flashover and should extend close enough -to the anode 28 to insure a shortenough path to the uns'heathed portion of the lead-in tube to preventash over. The space tube 3l is an additional safeguard and also helps to-support the disc 35. For ex'- ample, my tube may use `an anode voltageas high as 16,000 volts without flash over under these conditions. Thedistance from the anode 2-8 to the outer edge 5510i seal 3D should bequite long to prevent electrolysis `at l the seal. For the voltage used,I nd a distance of about '7.2 cm.

ill)

4 to be suiiicient. The distance inside the tube from the anode 28 tothe inner edge 59 of the seal is more important, and should be about 5.3cm. for the voltage used.

The tube may be made somewhat shorter by making the seal in a reentrantform as shown inFJgure.2. Inthis case `the-tube 58 extends into theenclosing .envelope and outward ,again as tube 3l to be sealed to thesheath 29 at point 59, which then extends upward out of the tube. Thegrid support collar 34 is then attached to the reentrant -ltube 58 asshown.

.The oxides in .the `coating on cathode I3 may,

ofcourse, beappliedias carbonates and converted .to eche oxides .b ycheating during exhaust in the manner Well-known to the art.

When not carrying current the voltage drop :across-.theztube may be16,000 volts, but when application of suiicient Woltage to the grid 36causes the .tube .to nre .and vpass current, the voltage across the tube.may .be .as low as 100 volts .or .less .fora .current .of 3.0.0.amperes the remainlng voltage .appearing in .the .load circuit. 'I he'grid voltage for ring the tube may be about volts in some cases,although it is genorally applied in .such transient .formas `to make its.measurement .diiiicult AEhe voltages .and ,current here given .are forthe peak value of :the ,pulse through .the tube, as farfas theyvcanbeascertained. The average current through `the tube .may b e `less .thanan ampere.

What.1 ,claim is:

1. A thyratron comprising an enclosing glass envelope having a il-rsttubularreentrant portion and .a second tubular `portion reentrant intosaid first reentrant portion, a lead-in wire sealed through the end ofsaid second tubular portion and extending .into Asaid .envelope .for aconsiderable distance concentric withandspaced radially from 4saidsecond tubular portion, .a glass sheath extending along said wire andinside .but spaced radially from .said `second .tubular -portion .forsubstantially its entire length, an ranode in said envelope andsupported by., and .transverse to said leadin wire, a gridinside .theenvelope and surrounding .said anode and .supported yfrom said firsttubular reentrant portion by a collar thereon and :a oatl'lode4 .insaidenvelope.

2. .An electrode support. comprising an enclosing ,glass envelope, areentrant vtubular structure including .an .outer glass tube-joined toand extending into said .envelope and a second glass tube coaxiallywithin saidouter .tube ,and joined thereto at itsinner end, a .lead-inwire coaxially within said .second tube `and sealed thereto at the outer.end .of .sa-idsecond tube, and a glass sheath .extend-ingalong .and-incontact with said Wire for the .greater .part of thev length thereof.

3.. A thyratron comprising a `glass envelope, a leadfin Wire sealedV.therethrough and extending into said envelope a substantial .dista-nceand supporting .an electrode, a glass sheath sealed to said leadPin wirealong most of its length, a glass tubular structme .concentric with saidsheath and extending therealong from said envelope, and .anotherelectrode secured to said glass tubular structure at the innermost endthereof.

f4. A thy-ratron comprising an enclosing glass envelopehaving -areentrant tubular structure including an outer. glass tubeanda secondglass tube .coaxially wi-thinv said outer tube., said tubes boingvjoined together at their 4innermost ends, a lead-in wire coaxiallywithin said second tube and sealed thereto at the outermost end of saidsecond tube, a glass sheath extending along said lead-in wire for mostof its length inward from the point of sealingto said second tube, anelectrode joined to the innermost end o1" said lead-in Wire, and asecond electrode mechanically connected to and supported by theinnermost end of said reentrant tubular structure.

5. A thyratron comprising an enclosing envelope, an anode transverse tothe longitudinal axis of said envelope, a grid substantially surroundingsaid anode, an insulating tube sealed to said envelope and extendingthereinto, a lead-in Wire sealed to said tube and extending into saidenve lope coaxially Within said tube, an insulatingsheath sealed aroundsaid lead-in Wire for substantially the entire length of said tube, amechanical connection between said grid and said tube providing supportfor said grid, a cylindrical cathode with closed ends separated fromsaid anode by said grid, a coating of alkaline earth oxides on only thecylindrical sides of said cathode and terminating a short distance fromthe ends of the cylindrical sides thereof, said ends being free fromsaid oxides, a metal shield concentric with said cathode and spacedclosely Cil therearound and connected thereto, and a second metal shieldconcentric with said cathode and outside and around said first shieldand connected to said grid, the cathode and both metal shields beingconcentric with the longitudinal axis of the cylinder, said envelopehaving a filling of hydrogen.

HOWARD B. SLOAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

